Fugitive slaves in Virginia in about 1863, many of whom ended up in “contraband camps” near Union army bases where conditions were unsanitary and food limited. Photograph: Andrew J. Russell/Medford Historical Society Collection/CORBIS

Hundreds of thousands of slaves freed during the American civil war died from disease and hunger after being liberated, according to a new book.

The analysis, by historian Jim Downs of Connecticut College, casts a shadow over one of the most celebrated narratives of American history, which sees the freeing of the slaves as a triumphant righting of the wrongs of a southern plantation system that kept millions of black Americans in chains.

But, as Downs shows in his book, Sick From Freedom, the reality of emancipation during the chaos of war and its bloody aftermath often fell brutally short of that positive image. Instead, freed slaves were often neglected by union soldiers or faced rampant disease, including horrific outbreaks of smallpox and cholera. Many of them simply starved to death.